1. Field of the Invention
This invention relates to a polarization separator which separates orthogonal polarization electromagnetic waves propagating in a circular waveguide into a horizontal polarization wave and a vertical polarization wave, and more particularly to a polarization separator for use with a reception antenna or a like apparatus for broadcasting such as CS (Communication Satellite) broadcasting in Japan or ASTRA satellite broadcasting in Europe wherein horizontal polarization waves and vertical polarization waves are transmitted as orthogonal polarization waves modulated in various channels.
The present invention further relates to a converter integrated with a polarization separator suitable to receive broadcasting of the type mentioned and an output waveguide-microstrip line mode transformer for a polarization separator for use with the converter.
2. Description of the Related Art
Various broadcast waves are transmitted from artificial satellites floating at the height of 36,000 Km from the ground. Of such broadcast waves, CS broadcast waves for commercial use can be received in Japan in addition to BS (Broadcasting Satellite) broadcast waves for use for television broadcasting.
A broadcasting frequency band of microwaves or quasi millimeter waves (SHF) is utilized for such broadcast waves. The broadcast waves are received by means of a parabola antenna normally installed on the roof, converted into predetermined frequencies by a converter and inputted to a tuner by which a broadcasting channel is selected.
A parabola antenna for receiving orthogonal polarization waves of the CS broadcasting or the ASTRA satellite broadcasting from among various broadcast waves is typically constructed in such a manner as shown in FIG. 8. Referring to FIG. 8, the parabola antenna shown includes a parabola reflector 81 for reflecting and converging radio waves from a satellite, a primary horn 83 for receiving the thus converged radio waves, a polarization separator 1 for separating the orthogonal polarization radio waves received by the primary horn 83 into horizontal polarization waves and vertical polarization waves, and a down converter 84 for converting the horizontal polarization waves and the vertical polarization waves separated by the polarization separator 1 for individual channels by frequency conversion and supplying signals obtained by the frequency conversion to a television tuner not shown.
Various polarization separators are conventionally employed for the polarization separator 1 in such an antenna for receiving the CS broadcasting as shown in FIG. 8 or a parabola antenna for receiving the ASTRA broadcasting. An exemplary one of such conventional polarization separators is shown in FIGS. 1 and 2A to 2C. FIG. 1 is a perspective view of the conventional polarization separator, and FIGS. 2A to 2C are a front elevational view, a longitudinal sectional view and a top plan view, respectively, of the conventional polarization separator.
Referring first to FIG. 1, the polarization separator shown includes a substantially tubular member 1 and separates orthogonal polarization waves received by a CS broadcasting reception antenna or an ASTRA broadcasting reception antenna into a horizontal polarization wave component H and a vertical polarization wave component V. The tubular member 1 has a circular waveguide 4 formed therein for propagating the orthogonal polarization waves therein. The circular waveguide 4 has a flange 2 to which the primary horn 83 shown in FIG. 8 is securely connected. A plurality of through-holes 3 are formed in the flange 2, and bolts not shown for securing the primary horn 83 shown in FIG. 8 are fitted in the through-holes 3. The tubular member 1 further has a rectangular opening 5 formed therein. The rectangular opening 5 has a major side in the direction of an axis of the circular waveguide 4 and serves as a horizontal polarization wave output terminal from which the separated horizontal polarization wave component H is extracted. A reflection plate 6 is located in the inside of the circular waveguide 4 and reflects only the horizontal polarization wave component H. The tubular member 1 further has a vertical polarization output terminal 7 from which the vertical polarization wave component V is extracted.
Orthogonal polarization waves received by the CS broadcasting reception antenna or ASTRA broadcasting reception antenna are introduced in the directions of orthogonal arrow marks V and H shown in FIG. 1 into the tubular member 1 of the polarization separator by way of the primary horn 83.
When the orthogonal polarization waves propagate in the circular waveguide 4 and reach the reflection plate 6 as indicated by arrow marks in FIG. 1, the horizontal polarization wave component H of the orthogonal polarization waves is reflected by the reflection plate 6 placed horizontally in the circular waveguide 4 so that it is outputted as indicated by an arrow mark H in FIG. 1 from the output terminal 5 in the form of a rectangular opening having a major side in the direction of the axis of the circular waveguide 4.
Meanwhile, the vertical polarization wave component V of the orthogonal polarization waves is not reflected by the reflection plate 6 since it is orthogonal to the reflection plate 6. Consequently, the vertical polarization wave component V propagates straightforwardly in the circular waveguide 4 and is outputted as indicated by an arrow mark V in FIG. 1 from the output terminal 7 of the circular waveguide 4.
It is to be noted that, since the output terminal 5 in the form of a rectangular opening has a cutoff structure (this will be hereinafter described) as viewed from the vertical polarization wave component V, the vertical polarization wave component V is not outputted from the output terminal 5.
As can be recognized from the structure described above, the conventional polarization separator separates orthogonal polarization waves into a horizontal polarization wave component H and a vertical polarization wave component V while the orthogonal polarization waves propagate in the polarization separator.
Further, in the polarization separator, propagation of the horizontal polarization wave component H toward the output terminal 7 is prevented by the reflection plate 6 which reflects the horizontal polarization wave component H in principle. Therefore, in order to sufficiently suppress the horizontal polarization wave component H from leaking to the output terminal 7 to assure a high separation efficiency of the polarization separator, the reflection plate 6 is formed long so as to increase the reflection efficiency of it.
FIG. 17 generally shows in perspective view an exemplary one of conventional down converters for converting radio waves received by a parabola antenna into a predetermined frequency by down conversion. Referring to FIG. 17, the down converter shown includes a waveguide member 110 having a waveguide entrance located at a focal position of a parabola antenna not shown, and a shield case 111 in which the waveguide 110 is accommodated integrally.
A waveguide-microstrip mode transformer section 112 which will be hereinafter described is incorporated in the inside of the shield case 111. A broadcasting signal extracted from the transformer section 112 is converted into a signal of a predetermined intermediate frequency by a microwave integrated circuit (MIC) provided on a circuit board 113 made of Teflon or a like material and is then connected to a tuner by way of a connector not shown.
Such a pair of signal circuits for converting a channel frequency of a horizontal polarization wave S.sub.H and a vertical polarization wave S.sub.V as shown in FIG. 18 are located on the circuit board 113, and each of the signal circuits includes a low noise radio frequency amplifier (RF amplifier), a local oscillator (OSC), a mixer (MIX) and an intermediate frequency amplifier (IF/AMP). The signal circuits and function circuits which include a stabilized power source section and so forth are disposed on a wiring pattern constructed as a distributed constant circuit on the circuit board 113.
Thus, the converter is constructed such that it separates received radio waves into horizontal polarization waves and vertical polarization waves in the waveguide of the waveguide member, processes thus separated signals S.sub.H and S.sub.V by the two respective signal circuits to obtain two intermediate frequency outputs IF1 and IF2 and supplies the intermediate frequency outputs IF1 and IF2 to a tuner on the reception side by way of a cable.
As well known in the art, two dc voltages DC1 and DC2 for driving the converter are supplied from the tuner side to the stabilized power source and supply power to the stabilized power source section each by way of a coil L and a diode D.
FIGS. 19A and 19B show a sectional view and a top plan view of the transformer section 112 from which electromagnetic waves having propagated in the waveguide 110 are extracted by means of a microstrip line.
Referring to FIGS. 19A and 19B, a central conductor 113A of a microstrip line printed on the circuit board 113 is partially inserted by a predetermined length as a probe in an internal space 112A of the transformer section 112 through an opening 112B formed in the transformer section 112. A grounding conductor (grounding conductor on the rear face of the circuit board 113) 113B constitutes the microstrip line and is removed at a portion 113D thereof in the inside of the waveguide 110 (transformer section 112).
The conventional polarization separator is disadvantageous in that, since the reflection plate 6 in the circular waveguide 4 must necessarily have a great length so as to assure a high separation efficiency, the circular waveguide 4 has a great length particularly in the axial direction, and this makes it difficult to minimize the entire polarization separator 1.
Further, though not shown, since a rectangular waveguide member is connected to the outside of the rectangular output terminal 5 of the tubular member 1, the opening of the output terminal 5 must have a sufficiently great size. Since the opening has a great size, the electromagnetic field in the circular waveguide 4 adjacent the opening is disordered in distribution, and this results in production of a reflection wave to return to the input terminal of the circular waveguide or in leakage of orthogonal polarization waves between the output terminals 5 and 7. Accordingly, there is a problem in that it is difficult to assure a high separation efficiency of the polarization separator.
Furthermore, since the polarization separator and the converter are coupled to each other at an end portion of the polarization separator adjacent the output waveguide member, there is another problem in that they are complicated in structure and great in number of parts and requires much time to produce and assemble them.
By the way, if the circuit board 113 in the converter is formed as a multi-layer circuit board, then the entire converter can be reduced in size and the mounting density of MIC (microwave integrated circuit) parts installed on the circuit boards can be increased and besides the conversion gains of signals can be enhanced.
FIG. 20 shows a sectional view where a two-layer circuit board is used to construct a waveguide-microstrip line mode transformer section, and in FIG. 20, like elements to those of FIG. 19 are denoted by like reference characters.
Referring to FIG. 20, a multi-layer circuit board assembly is composed of a circuit board 113 made of Teflon and another circuit board 114 made of glass, an epoxy resin or a like material and is inserted in an opening 112B at an end face of a waveguide member 112. A grounding conductor portion of the multi-layer circuit board assembly is removed so that electromagnetic waves in the inside of the waveguide member 112 are extracted from a center conductor 113A of a microstrip line formed on the circuit board 113. In this instance, there is a problem in that electromagnetic waves leak to the outside from a joining location between the second circuit board 114 and a portion of the waveguide member 112.
It is to be noted that the grounding conductor 113B has a thickness of 70 .mu.m, and it is difficult to scrape off only the second circuit board layer 114 leaving the grounding conductor 113B to obtain such a structure as shown in FIG. 19.